Moving subnets from one area to another in OSPF

[gdtmorgan]

I have taken over a beautiful lab that is already configured. In the public space I have 4 C Class subnets divided between Areas 0, 65 and 165. Growth has been different than planned and I need to move a /25 subnet from area 65 to 165. How?

Thank you.

[jackyoung · Accepted solution]

Can you explain the question in details ? If you only want to use more IP subnet, simply configure another class C. If you want to make one /25 subnet, you only need to configure this /25 subnet & interfacef in 165 and keep the config in 65. Because /25 will be more specify route in 165 that 65 will learn it from 165.

However, prepare a better IP address assignment will be easier for future move & change.

[gdtmorgan]

Sorry. I want to move the last half of the last Class C put in 65 to 165. In other words, its in area 65 now. I want to take it out and put it in area 165, permanently. The class C's are x.x.35.0, x.x.36.0, x.x.47.0 and x.x.48.0. I want to move x.x.48.128/25 from area 65 to area 165. The config's were established before I got here.

[jackyoung]

According to the subnet, you only need to add the "network x.x.48.128 0.0.0.127 area 165" in area 165 router then it is fine. It was because it is more specify (longer mask). If you want to be more consisitent, then change the command in area 65 router from "network x.x.48.0 0.0.0.255 area 65" to "network x.x.48.0 0.0.0.127 area 65".

After you configure the network command in both routers, remember not to use x.x.48.128/25 address in area 65 hosts.

Hope this helps.